Free piston engine



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FREE PISTON ENGINE Filed Sept. 28, 1956 2 Sheets-Sheet 1 INVEN 0R5 May13, 1958 Filed Sept. 28, 1956 C. F. BACHLE ETAL FREE PISTON ENGINE I 2Sheets-Sheet 2 iv R? IV ng/ INVENTORS CARL F. BACH LE BY EARL R. KLINGEATTo R EYS United States Patentfifice FREE PISTON ENGINE Carl F. Bachle,Grosse Pointe, and Earl R. Klinge, Harper Woods, Mich., assignors toContinental Aviation & Engineering Corporation, Detroit, Mich., acorporation of Virginia Application September 28, 1956, Serial No.612,617 8 Claims. (Cl. 123.41.35)

The present invention relates to internal combustion engines of the freepiston type, and more particularly to a means for altering the freepiston reciprocating cycle frequency for various engine operatingranges.

In the development of free piston engines capable of operating atrelatively high speeds, the reciprocating cycle frequency of the freepiston is determined by a number of factors, including the mass of thepiston, its stroke, and the volumes of the combustion chamber cylinder,the air compressor cylinder, and the bounce chamber. A major problemencountered is the relatively high and uneconomical fuel consumption atidling operation, since' the reciprocating cycle frequency remains atthe relatively high value determined by the above recited factors.

An object of the present invention is to attain more economical fuelconsumption during free piston idling operation by providing a means forincreasing the mass of the piston to reduce reciprocating cyclefrequency thereof.

Another object of the present invention is to provide a free pistonengine with controllable piston reciprocating cycle frequency byconstructing a chambered piston having a means for selectively fillingsame with liquid to increase its mass during engine idling operation.

A further object of the present invention is to provide a free pistonengine with a variable mass piston by constructing a chambered pistonhaving liquid coolant passages opening into the piston chamber andproviding means for selectively trapping a required amount of coolant inthe chamber.

For a more detailed understanding of the invention, reference may be hadto the accompanying drawings illustrating a preferred embodiment of theinvention in which like characters refer to like parts throughout theseveral views and in which Fig. 1 is a cutaway longitudinal sectionalview of a preferred type of free piston engine utilizing the presentinvention and including a diagrammatic representation of a source ofcoolant supply.

Fig. 2 is a sectional view taken substantially on the line 2-2 of Fig.1, and

Fig. 3 is a sectional view taken substantially on the line 3-3 of Fig.1.

A preferred type of free piston engine is illustrated as having athree-step cylinder structure comprising a -combustion chamber cylinder11, an air compressor cylinder 12, and a bounce chamber cylinder 13. Thebounce chamber is contained by an engine cylinder head 10a. A freepiston structure 14 preferably comprising a power piston portion 15 anda larger air compressor piston portion 16, reciprocates in thecombustion chamber cylinder and the air compressor cylinderrespectively. A chamber 17 in the piston comprises a power pistoncompartment 17a and a compressor piston compartment 17b, which areopenly connected by ports 18 shown in Figs. 1 and 2. This compartmentedchamber 2,834,329 Patented May 13, 1958 17 is adapted to trap liquidcoolant for increasing the mass of the piston.

The power piston portion 15 is provided with an annular coolant passage20 connected to a central axially extending tube 21. Liquid coolant ispreferably supplied from a cooler and reservoir structure 22, and ispumped by a pump 23 through a conduit 24 to an intake duct 25 extendingaxially into the end of the engine 10, and through the center of thecompressor piston portion 16, terminating just short of the inner end ofthe power piston portion 15 when the piston is at the outermost limit oftravel. The tube 21'is adapted to slide within the duct 25 as the piston14 reciprocates, so that the coolant passage 20 will be continuouslysupplied with liquid coolant.

After circulation through the passage 20, the coolant passes throughports 26 into the chamber 17. Drain tubes 27 are secured to the pistonportion 16 and extend into drilled bores 28 in the cylinder head 100. Asthe piston 14 reciprocates, the tubes 27 slide in the bores 28,maintaining continuous contact therewith. An upper drain conduit 30 isconnected by suitable fittings and passages to the upper bore 28 in thecylinder head and lower drain conduit 31 is similarly connected to thelower bore 28. The two conduits 30 and 31 are connected with aT-coupling or union 32 and drained coolant is returned through a conduit33 to the cooler and reservoir 22. A valve 34 is provided in the lowerconduit 31.

During normal engine operation at speeds above idling, the liquidcoolant circulating through the passage 20 and passing into the chamber17 is drained off through the lower conduit 31, the valve 34 being in anopen position. The mass of the piston 14 will consequently be at aminimum and the reciprocating cycle frequency will be at a maximum. Asthe engine is idled, the valve 34 will be closed, either manually orbyany suitable automatic means. The liquid will then be trapped, and willfill both the large compartment 17b and the small compartment 17a of thechamber 17. When substantially completely filled to the level of theupper drain tube 27, the coolant will then continue to drain through theconduit 39, providing for continuous circulation through the system.With the piston now filled with liquid, its mass is correspondinglyincreased and the reciprocating cycle frequency is reduced to a minimumfor more economical operation of the engine.

Although but one preferred embodiment of the invention has beendescribed herein, it will be apparent to one skilled in the art to whichthe invention pertains that various changes and modifications may bemade therein without departing from the spirit of the invention or thescope of the appended claims.

We claim:

1. In an internal combustion engine of the free piston type and having acylinder structure, a free piston reciprocating in said cylinderstructure, a chamber in said piston, means connecting said chamber witha source of liquid supply, and means selectively operable to trap adesired amount of liquid in said chamber whereby to change the mass ofsaid piston and alter the reciprocating cycle frequency thereof.

2. In an internal combustion engine of the free piston type and having acylinder structure, a free piston reciprocating in said cylinderstructure, a chamber in said piston, means connecting said chamber Witha source of liquid supply, and controllable outlets from said chamberfor varying the amount of liquid trapped in said chamber whereby tochange the mass of said piston and alter the reciprocating cyclefrequency thereof.

3. In an internal combustion engine of the free piston type and having acylinder structure, ,a free piston reciproof liquid trapped in. said.chamber whereby to change the mass of said piston and alter thereciprocating cycle frequency thereof, said last mentioned meanscomprising a plurality of, outlets from various levels. of said chamaher, and valve means selectively closing the lowerlevel outletto, trap acontrolled amount ofv liquidinsaidchamber.

4'. Man internal combustionengine of the free piston type and having acylinder structure, afree piston reciprocating in said cylinderstructure, a chamber in said piston,,means connectingsaidchamber with a:source of liquid supply, and. means selectively operable to vary theamount, of. liquid trapped insaid chamber whereby to change the mass of.said piston and alter the reciproeating cycle frequency thereof, saidlast mentioned means comprisingupper and lowerv outlets from saidchamber, and valve means selectively closing saidlower outlet to trapliquid in, said chamber 'to the height of saidupper outlet.

5. In an internal combustion engine of the free piston type and having,a. cylinder structure, a free piston reciprocating in said cylinderstructure, a chamber in said piston, means connecting said chamber witha source of liquid supply, and means selectively operable to vary theamount. of liquid trapped insaid chamber whereby to change the mass ofsaid piston and alter the reciprocating cycle frequency thereof, saidlast mentioned means comprising upper and lower outletsfrom saidchamber, and valve means selectively closing said lower outlet to trapliquid in said chamber. to the height of said upper outlet, saidpistoncomprising'relatively small and large diameter portions, saidoutletsbeing in said large diameter portion.

6. In aninternal combustion engine of the freepiston type andhaving; acylinder structure, a free piston reciprocating in said cylinder.structure, a coolant passage in: said piston, achamber. in said: pistonand openly connected with said coolant passage, means conducting coolantunder pressure into said coolant passage, and means selectively trappingvarying amounts of coolant in said chamber whereby to change the mass ofsaid piston and alter the reciprocating cycle frequency of same.

7. In an internal combustion engine of the free piston type and having acylinder structure, a free piston reciprocating. in said: cylinder.structure, a chamber in said piston, means connectingsaid chamber withasource of liquid supply, andimeansselectively operable to vary theamount of liquid trapped in said chamber: whereby. to change the mass ofsaid piston and. alter the reciprocating cycle frequency thereof, saidcoolant trapping means comprising a plurality of' drairrv outletslocated at various levels of said chamber, and valve means selectivelyoperable to close one or more of said drain outlets to control. theamountof coolant trapped in said chamber.

8. In, an internal combustionengine of the-free piston type and havinga, cylinder structure, a free piston reciprocating in said cylinder.structure, a chamber in said piston, means connecting saidchamber with asource of liquid supply, and controllable outlets from said chamber forvarying the amount of liquid trapped in, said chamber whereby to changethe mass-of said piston and alter the reciprocating cycle frequencythereof, said valve means normally. open. for engine high speedoperationto maintain substantially aminimum'of coolantin said chamher. andthereby attain a maximum reciprocating. cycle frequency of saidv piston,and. said valve means closing. the lower. level outlet: for engine idleoperationltomaintain substantially a maximum of coolant in said chamberandthereby attain aminimum reciprocating cycle frequency of said piston;

References Cited inthe'file of this patent.

UNITED STATES PATENTS 2,645,213. Huber July 14, 1953

